EP3682276A1 - Procédé et appareil de connexion à alignement automatique de fibre à un guide d'ondes de circuit intégré photonique - Google Patents

Procédé et appareil de connexion à alignement automatique de fibre à un guide d'ondes de circuit intégré photonique

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Publication number
EP3682276A1
EP3682276A1 EP18786457.4A EP18786457A EP3682276A1 EP 3682276 A1 EP3682276 A1 EP 3682276A1 EP 18786457 A EP18786457 A EP 18786457A EP 3682276 A1 EP3682276 A1 EP 3682276A1
Authority
EP
European Patent Office
Prior art keywords
waveguide
core
fiber
target
input fiber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP18786457.4A
Other languages
German (de)
English (en)
Inventor
Liming Wang
Martin A. Kits Van Heyningen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
KVH Industries Inc
Original Assignee
KVH Industries Inc
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Filing date
Publication date
Application filed by KVH Industries Inc filed Critical KVH Industries Inc
Publication of EP3682276A1 publication Critical patent/EP3682276A1/fr
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/30—Optical coupling means for use between fibre and thin-film device
    • G02B6/305—Optical coupling means for use between fibre and thin-film device and having an integrated mode-size expanding section, e.g. tapered waveguide
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/30—Optical coupling means for use between fibre and thin-film device
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
    • G02B6/2826—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals using mechanical machining means for shaping of the couplers, e.g. grinding or polishing

Definitions

  • the following relate to evanescence wave coupling connection between optical fibers, or an optical fiber to a photonic integrated circuit (PIC) waveguide, or between PIC waveguides.
  • PIC photonic integrated circuit
  • U. S. Patent 4,678,267 describes coupling between narrow-and wide-channel optical waveguides is found to be very efficiently performed by coupling regions in the form of parabolas. Design equations for parabolic coupling regions are given.
  • U. S. Patent 5,579,424 describes an arrangement for optically coupling a planar optical waveguide and an optical fiber.
  • the arrangement comprises forming a planar optical waveguide on a surface of the substrate, forming a trench-like depression in the surface of the substrate leading from an end face of the planar waveguide to an edge of the substrate, forming a second holder part having a fiber secured between two planar surfaces lying in a common plane, and assembling the separate holder part on a pair of planar surfaces lying on each side of the depression of said substrate so that the fiber is placed in the depression with play and the fiber will be arranged with the axis of the fiber being aligned with the axis of the planar waveguide.
  • U. S. Patent 5,600,745 describes a method of automatically coupling between a fiber and an optical waveguide. Such a scheme is achieved by the property of the different etching rates in the various wafer directions on a semiconductor material, especial silicon, and the shrinking property of the glass soot formed by a flame hydrolysis deposition technique during a high temperature consolidation process, for improved aligning accuracy.
  • a waveguide buffer layer is formed on a semiconductor substrate, then a waveguide layer is formed on the semiconductor substrate and the waveguide buffer layer.
  • a part of the waveguide is manipulated t th l ti l id M hil l i d hi h l d to the I/O end of the the windows is etched anisotropically to form several aligning grooves.
  • the lateral faces of these grooves and the surface of the semiconductor substrate can constitute a fixed angle.
  • U. S. Patent 5,729,641 describes an optical device for modulating or interacting with radiation guided and propagating along an optical longitudinal axis of an optical waveguide, such as, an optical fiber, has a different directional geometry compared to conventionally comparable devices such as, for example, plasmon or planar surface modulators for optical fibers.
  • the geometry includes a nonlinear, electro-optic medium formed between two spatially disposed electrodes. The medium/electrode sandwich is aligned along the waveguide
  • An applied electric field to the spatially disposed electrodes varies the refractive index of the electro-optic medium from just below the effective refractive index of the waveguide to just above the effective refractive index waveguide to induce a lossy condition on the propagating radiation. Modulation of the applied electric field will bring about intensity modulation of the propagating radiation.
  • U. S. Patent 5,982,961 describes an optical coupling device, or a compound waveguide, in which optical energy is coupled to or from an optical signal propagating along a transmitting waveguide.
  • the optical coupling device includes a thin film organic crystal waveguide positioned in optical proximity to a portion of the transmitting waveguide.
  • the organic crystal waveguide has a first, coupling surface facing the transmitting waveguide through which the optical energy is coupled.
  • the transmitting waveguide may be a fiber optic having at least some material removed along a side thereof to facilitate the coupling of optical energy between the fiber optic and the organic crystal waveguide. Polishing and lapping methods for producing the thin film organic crystal waveguide, with optically smooth surfaces, are also disclosed, as are organic salt implementations of the organic crystal.
  • U. S. Patent 6,293,688 describes a tapered waveguide that couples optical waveguides of different sizes in a multi-chip optical assembly.
  • a resonator containing a semiconductor diode amplifier is coupled to a planar waveguide structure that optically couples to an optical fiber.
  • a single-mode semiconductor laser waveguide is flip-chip bonded to a substrate and couples to a silica waveguide structure that couples to a single-mode tantala waveguide.
  • high-index material is provided in a gap between chips.
  • polymer material is used in the waveguide structure to modify thermal characteristics of the [0009] U. S.
  • Patent 6,360,038 describes a wavelength-selective optical device for coupling of light at predetermined wavelength from one optical fiber waveguide to another using at least two gratings and cladding-mode assisted coupling is disclosed.
  • the transfer of light is performed using intermediate coupling to one or more cladding mode of the waveguides.
  • an arrangement for transfer of light from one cladding to another is required.
  • the disclosed coupler has no back-reflection, small insertion loss, and very high channel isolation.
  • the device can be used in wavelength-division
  • U. S. Patent 7,218,809 describes an optical mode transformer comprising a waveguide core having a high refractive index contrast between the waveguide core and the cladding, the optical mode transformer being configured such that the waveguide core has a taper wherein a thickness of the waveguide core tapers down to a critical thickness value, the critical thickness value being defined as a thickness value below which a significant portion of the energy of a light beam penetrates into the cladding layers surrounding the taper structure thereby enlarging the small mode size.
  • This patent further describes a non-cylindrical graduated refractive index (GRID) lens structure.
  • GRID non-cylindrical graduated refractive index
  • the grading of the refractive index is provided in a either the vertical or horizontal directions and may have either a fixed refractive index or a graded refractive index in the transverse directions.
  • This patent further describes composite optical mode transformers that are combinations of the taper waveguide structures and the non- cylindrical graduated refractive index structures.
  • This patent further describes the further integration of the mode transformers with V-grooves for multiple input/output fibers and alignment platform for multiple input/output photonic chips or devices.
  • the described embodiments facilitate a self-alignment mechanism between the optical fiber and the photonic integrate waveguide and pertains to the connection of a single- mode optical fiber to a single-mode waveguide of photonic integrate circuit waveguide passively with high coupling efficiency and wide bandwidth.
  • the described embodiments are directed to an optical device that comprises an input fiber having a cladding and a core for providing a light input, and a target photonic integrated circuit (PIC) waveguide having a cladding and a core for receiving a light input.
  • PIC photonic integrated circuit
  • the cladding on one side of the input fiber is removed at the end of the fiber and a flat surface is created along h f h fib respect to the symmetric axis of the PIC waveguide is fabricated on the top cladding layer of the PIC waveguide in the coupling area, so the upper surface of the tapered planar waveguide is therefore exposed.
  • the flat surface of the input fiber and the top surface of the target waveguide is contacting, so the core of the input fiber being intersected with an angle with respect to the symmetric axis of the target waveguide and close together at the intersect as an interacting region to define a hybrid waveguide.
  • the invention may be an optical device compromising an input fiber configured to provide a light input.
  • the input fiber may have a cladding and a core, with the cladding on one side of the input fiber removed at an end of the input fiber, thereby creating a flat surface along the input fiber for a predetermined distance.
  • the flat surface may be configured to be close to the core of the fiber such that the fiber core is exposed.
  • the optical device may further comprise a target photonic integrated circuit (PIC) waveguide configured to receive the light input.
  • the target PIC waveguide may be planer and have a top cladding layer and a core.
  • the optical device may further comprise a flat-bottomed channel fabricated on the top cladding layer of the target PIC waveguide in a coupling area, such that the upper surface of the target PIC waveguide is exposed.
  • the flat surface of the input fiber may be configured to contact the top surface of the target PIC waveguide such that the core of the input fiber and the core of the target PIC waveguide are close and in parallel to each other in the coupling area to form a hybrid waveguide.
  • the optical device may further comprise a first transition for coupling of light from the input fiber to the hybrid waveguide, and a second transition for coupling of light from the hybrid waveguide to the target PIC waveguide.
  • the coupling area may be configured to be between the first transition and the second transition in a lengthwise direction within a plane of the PIC waveguide.
  • the core of the target PIC waveguide may have a higher refractive index than a refractive index of the core of the input fiber.
  • the core of the target PIC waveguide may be silicon nitride and the cladding of the target PIC waveguide may be silicon oxide.
  • the target PIC waveguide may be birefringent.
  • the input fiber may be a polarization maintaining fiber. A portion of the core of the input fiber may be removed within the coupling region.
  • the first transition may be a start end of the target PIC waveguide, and the second transition may be a tip of the input fiber.
  • the core of the target PIC waveguide may have a lower refractive index than a refractive index of the core of the input fiber.
  • the invention may be an optical device compromising an input fiber d Th creating a flat surface along the input fiber for a predetermined distance.
  • the flat surface may be configured to be close to the core of the fiber such that the fiber core is exposed.
  • the optical device may further comprise a target photonic integrated circuit (PIC) waveguide configured to receive the light input.
  • PIC photonic integrated circuit
  • the target PIC waveguide may be planer and have a top cladding layer and a core.
  • a width of the core of the target PIC waveguide may be configured to become gradually narrow along its length, symmetrically with respect to the center axis, to define an in- plane taper.
  • the optical device may further comprise a flat-bottomed channel fabricated on the top cladding layer of the target PIC waveguide in a coupling area, such that the upper surface of the target PIC waveguide is exposed.
  • the flat surface of the input fiber may be configured to contact the top surface of the target waveguide, such that the core of the input fiber and the core of the target PIC waveguide are close and in parallel to each other in the coupling area to form a hybrid waveguide.
  • the optical device may further comprise a first transition for coupling of light from the input fiber to the hybrid waveguide, and a second transition for coupling of light from the hybrid waveguide to the target PIC waveguide.
  • the coupling area may be configured to be disposed between the first transition and the second transition in a lengthwise direction within a plane of the PIC waveguide.
  • the invention may be an optical device compromising an input fiber configured to provide a light input.
  • the input fiber may have a cladding and a core.
  • the cladding on one side of the input fiber may be removed at an end of the input fiber thereby creating a flat surface along the input fiber for a predetermined distance.
  • the flat surface may be configured to be close to the core of the fiber such that the fiber core is exposed.
  • the optical device may further comprise a target photonic integrated circuit (PIC) waveguide configured to receive the light input.
  • the target PIC waveguide may be planer and have a top cladding layer and a core.
  • the optical device may further comprise a flat-bottomed channel fabricated on the top cladding layer of the target PIC waveguide in a coupling area, such that the upper surface of the target PIC waveguide is exposed.
  • the flat-bottomed channel may have an in-plane angle with respect to a symmetric axis of the PIC waveguide.
  • the flat surface of the input fiber may be configured to contact the top surface of the target PIC waveguide, such that the core of the input fiber and the core of the target PIC waveguide are close and in parallel to each other in the coupling area to form a hybrid waveguide.
  • the optical device may further comprise a first transition for coupling of light from the input fiber to the hybrid waveguide, and a second transition for coupling of light from the hybrid waveguide to the target PIC waveguide.
  • the d h d [0018]
  • the invention may be an optical device compromising an input fiber configured to provide a light input.
  • the input fiber may have a cladding and a core.
  • the cladding on one side of the input fiber may be removed at an end of the input fiber, thereby creating a flat surface along the input fiber for a predetermined distance.
  • the flat surface may be configured to be close to the core of the fiber such that the fiber core is exposed.
  • the optical device may further comprise a target photonic integrated circuit (PIC) waveguide configured to receive the light input.
  • PIC photonic integrated circuit
  • the target PIC waveguide may be planer and having a top cladding layer and a core.
  • a width of the core of the target PIC waveguide may be configured to become gradually narrow along its length, symmetrically with respect to the center axis to define an in- plane taper.
  • the optical device may further comprise a flat-bottomed channel fabricated on the top cladding layer of the target PIC waveguide in a coupling area, such that the upper surface of the target PIC waveguide is exposed.
  • the flat surface of the input fiber may be configured to contact the top surface of the target waveguide such that the core of the input fiber and the core of the target PIC waveguide are close and in parallel to each other in the coupling area to form a hybrid waveguide.
  • the optical device may further comprise a first transition for coupling of light from the input fiber to the hybrid waveguide, and a second transition for coupling of light from the hybrid waveguide to the target PIC waveguide.
  • the coupling area may be configured to be between the first transition and the second transition in a lengthwise direction within a plane of the PIC waveguide.
  • FIG.1 shows an optical fiber with cladding removed to form a flat surface, according to an embodiment of the invention.
  • FIG.2 shows a PIC waveguide with cladding removed from atop the waveguide core, according to an embodiment of the invention.
  • FIG.3 shows a plan view of a flat-surfaced optical fiber disposed on a PIC
  • FIG.4 shows a top view of the optical fiber and PIC waveguide shown in FIG.3,
  • FIG.5 shows a hybrid waveguide formed according to an embodiment of the invention.
  • FIG.6 shows an optical fiber disposed on a PIC at an angle ⁇ ⁇ , according to an embodiment of the invention.
  • FIG.7 shows a plot of the waveguide width as a function of z at different crossing angles ⁇ ⁇ , according to an embodiment of the invention.
  • FIG.8 shows a plot of the waveguide width as a function of z at different values of the constant ⁇ , according to an embodiment of the invention.
  • FIG.9 illustrates the simulated optical powers guided by the fiber, the PIC waveguide and the total optical fiber for an example embodiment of the invention.
  • FIG.10 illustrates the dependency of coupling efficiency on wavelength, according to an example embodiment of the invention.
  • FIG.11 shows alignment tolerance for positioning the fiber onto the waveguide taper, according to an example embodiment of the invention.
  • FIG.12 shows a flat-surfaced optical fiber with a portion of its core also removed, according to an embodiment of the invention.
  • FIG.13 shows coupling efficiency of an optical fiber as illustrated in FIG.12.
  • FIG.14 illustrates an optical fiber being coupled to a PIC waveguide according to an embodiment of the invention.
  • the described embodiments are directed to photonic integrated circuits. More particularly, described embodiments pertain to the connection of a single-mode optical fiber to a single-mode waveguide of photonic integrate circuit waveguide passively with high coupling efficiency and wide bandwidth, and to the use of such devices for optical gyroscopes and optical communications.
  • An optical fiber 100 guiding light in single- mode spatial distribution consists of glass core 104 that has a higher refractive index than that of the surrounding glass cladding 106.
  • the optical fiber has a predetermined dimension of the glass core, and the difference of the refractive index between the glass core 104 and cladding 106 such that the waveguide supports only the fundamental mode.
  • the glass cladding on one side of the optical fiber is removed and a flat surface 102 is created along a fiber core 104 for a predetermined distance, as shown in FIG.1.
  • the flat surface 102 is made close to the core 104 of the fiber 100 such that the fiber core 104 is exposed.
  • the evanescent optical wave of the guided light is extended beyond the flat surface 102 of the cladding material, and the percentage of the light power that is distributed beyond the flat surface 102 is dependent on the refractive index of the material that replacing the original cladding glass.
  • a single-mode optical waveguide of a PIC consists of a waveguide core that is buried into cladding material.
  • the core has a higher refractive index than that of the cladding material.
  • the PIC waveguide is configured to have a predetermined dimension of the core, and the difference of the refractive index between the core and cladding, such that the waveguide supports only the fundamental mode.
  • a predetermined area of cladding material atop the waveguide core 202 is removed to allow the electromagnetic wave of the guided light to extend into the material replaced by the cladding, as shown in FIG.2.
  • the evanescent optical wave of the guided light is extended beyond the top surface 204, and the percentage of the light power that is distributed beyond the top surface 204 is dependent on the refractive index of the material that replacing the original cladding material.
  • the waveguide core is silicon nitride
  • the cladding material is silicon oxide.
  • the waveguide core is a thin silicon nitride strip, the thickness of which is less than 100 micrometers.
  • the fiber section at the tip where the cladding material is removed is laid down in such a way that the flat surface is facing downwards and the core is aligned along the PIC waveguide in the area where the cladding of the planar waveguide is also removed, as shown in FIG.3.
  • the two cores of the waveguides are arranged close to each other such that there is large overlap of the two evanescent fields, so as to form a hybrid waveguide in the overlapping region.
  • the fiber core can be placed directly on the top of the PIC core, as shown in FIG.4 (viewed as a top view, looking down at the top surface of the PIC).
  • the hybrid waveguide supports a single mode light propagation, but with a different propagation constant from both the PIC waveguide and fiber waveguide.
  • the cross-section of the guided light beam changes abruptly when the beam transfers from the fiber to the hybrid waveguide and when from the hybrid to the PIC waveguide. The abrupt changes facilitate coupling of the lowest-order mode into a radiation mode, and may increase the transition loss. Fabricating the PIC waveguide in an optimized shape as described herein, on the other hand, may greatly reduce the transition loss.
  • the PIC waveguide width may be gradually tapered to a smaller width at the end.
  • a hybrid waveguide may be constructed by placing the cladding-removed fiber 104, with the flat surface facing downwards (i.e. toward the PIC substrate), close to and aligned along the tapered section 502 of the PIC waveguide 202 where the cladding of the PIC waveguide is also removed, facilitating a large overlap of the two evanescent fields.
  • the fiber core 104 can be placed right on the top of the tapered section 502 of the PIC core, and it can also be shifted sideways.
  • the hybrid waveguide changes the cross-section of a guided beam.
  • the guided light in the fiber waveguide is coupled into the hybrid waveguide though a transition of a gradual expansion of the effective guide cross-section. If this expansion is gradual enough (as set forth in more detail below), the fiber mode will progressively evolve into the lowest-order mode without mode conversion.
  • U.S. Patent No.4,678,267 discloses a simple design rule that ensures an adiabatic operation in a symmetric taper.
  • the lowest-order optical mode is well confined by a waveguide, so the lowest-order mode is well confined in the taper without mode conversion to higher-order modes or radiation modes, if the taper is designed to satisfy a condition defined by: ⁇ ⁇
  • ⁇ 2 ⁇ ⁇ ⁇ ⁇ ⁇ , (1)
  • ⁇ is a constant, less than or equal to unity, related to the rate of taper of the PIC waveguide core (discussed in more detail herein).
  • the parameter ⁇ is the local half angle of the taper
  • ⁇ is the wavelength in vacuum
  • ⁇ ⁇ ⁇ ⁇ is the mode effective index of the mode confined in the hybrid waveguide
  • ⁇ is the local full width of the taper.
  • the adiabatic propagation condition of Eq. (1) is obtained using a design criterion of a slower expansion of the waveguide width than the diffraction divergence of the lowest order mode. If ⁇ is larger than the divergence angle of the lowest mode in the ray model the ray would not“see” the waveguide sidewalls, and the phase front of the wave would become distorted and would result in mode conversion from the lowest-order mode.
  • Eq. (1) suggests that the local waveguide width expansion slope along the propagation direction, z, satisfies:
  • taper shape should be parabolic under the assumption that is a constant.
  • the example embodiments described herein present a procedure that enables the connection of an optical fiber to a PIC waveguide requiring a very low alignment accuracy, but resulting in a high coupling efficiency.
  • the procedure facilitates a passive and low-loss fiber to PIC waveguide connection.
  • the key arrangement is to place a core-exposed fiber on top of the taper area of the PIC waveguide with a predetermined crossing angle, as shown in FIG.6.
  • the projection of the ray angle of the lowest-order mode in the plane of the waveguide would not exceed the local angle of the wall of the waveguide.
  • the ray would be confined by the waveguide wall and the phase front of the wave would not become distorted.
  • FIG.7 is a plot of the W as a function of z at different crossing angles
  • FIG.7 indicates that a taper with slower width slope (i.e., more gradual width change) is required when the light is launched with an angle than that when the axes of the two cores are aligned in parallel. In other words, the larger the input angle is, the slower the taper is required.
  • FIG.8 is a plot of the W as a function of z at different values of ⁇ , where
  • a small ⁇ value means shorter effective
  • FIG.9 illustrates the simulated optical powers guided by the fiber, the PIC waveguide and the total optical fiber on one embodiment of the device.
  • the optical fiber has 4.3um x 4.3um mode field to the 1/e ⁇ 2 of the power, and the mode field for the output PIC waveguide has a mode field of 1.0um x 4.3um.
  • the core-exposed fiber is overlaid on the top of PIC waveguide taper with a shape described by Eq. (7).
  • the fiber axis is laid across the taper section with a 0.25 ° angle to the optical field at x-z view.
  • Legend 901 defines the shading shown in graphical display 900, with reference numbers 902, 904, 906, 908, 910 and 912 identifying reference points of the shading.
  • Plot 903 shows the results of percentage of light, normalized to the input power.
  • Line 920 is partial power propagating in the fiber core
  • line 922 indicates the partial power guided in the PIC waveguide core
  • line 924 indicates the total power.
  • the coupling efficiency is 98% from the fiber waveguide to the PIC waveguide in this embodiment.
  • the coupling efficiency is weakly dependent on the operation free space wavelength, as indicated in FIG.10.
  • the operation wavelength in FIG.10 ranges between 790 ⁇ 850nm. In this wavelength bandwidth, the coupling efficiency, or the normalized guide optical power, is higher than 0.98.
  • FIG.11 shows that alignment tolerance for positioning the fiber onto the taper is approximately 0.8mm to keep the coupling efficiency higher than 90%. This position accuracy is well achievable with a standard microfabrication technology.
  • the fiber flat surface needs to be overlaid onto the top surface of the PIC waveguide very closely.
  • the gap required to achieve a better than 90% coupling efficiency in this embodiment is less than 0.2 ⁇ m, which is difficult to realize due to various reasons, e.g., the possibility that the flat is unevenly micro-machined, or not applying enough pressing force to the fiber to overcome the counterforce from the surface tension of the bonding adhesive.
  • the cladding material of the mating fiber may be over-removed, such that a portion of the fiber core is also removed, as indicated in FIG.12. Using this type of over-etched fiber as an overlay on the in-plan tapered waveguide, the coupling efficiency is still larger than 90% if there is a 2.2 micron gap between the fiber flat and the PIC waveguide, as shown in FIG.13.
  • One technique is side- polished fibers made by embedding fibers in silicon V grooves and by polishing them
  • Another technique is to draw a D-shape fiber.
  • the process started with a preform made in the D-shape [see, e.g., T.D.Monte, L.Wang and R.Dyott“Elliptical Core and D-shape Fibers” in Specialty Optical Fibers Handbook, Amsterdam Boston Heidelberg London, eds.
  • A. cross-section profile of the preform is in D-shape.
  • the flat surface of the grounded preform is kept at enough of a distance from the waveguiding core such that no additional optical attenuation will be generated by the surface.
  • the D-shaped fiber preform is then drawn down size to single mode fiber.
  • a section of the D- shaped fiber must be further exposed.
  • the process for the fine removal of the cladding is usually carried out actively, such that the light is launched from one end of the fiber and the output power is monitored on the other end.
  • the degree of the cladding removal is in-situ monitored by the output power measurement.
  • the D-shaped fiber is chemically etched to a desired core exposure by chemicals such as glass etching creams, hydro fluoride acid and buffered hydro fluoride.
  • Fiber optical polarizers, two-by-two fused fiber couplers, and phase modulators have been demonstrated on these types of fiber [Liming Wang and Thomas D. Monte,“Phase modulation of an electro-optic polymer cladded polarization- maintaining optic fiber”, Optics Letters, 33, pp.1078-1080 (2008)].
  • FIG.14 depicts the coupling area 1402 where the D-shaped fiber 1404 is still separated from and above the PIC surface 1406.
  • a flat-bottomed channel may be fabricated on the top cladding layer of the PIC waveguide, the upper surface of the tapered core at the end of the planar waveguide is therefore exposed.
  • the channel may be made with width that allows the fiber to be tightly set into the channel, with the flat surface of the D-fiber in close contact with the top surface of the PIC waveguide.
  • An optically clear adhesive with a predetermined refractive index may be applied between the two surfaces, which keeps the fiber in place and supplies smooth refractive index transition between the two waveguides.
  • the channel can be fabricated along with the waveguide fabrication process, the PIC in-plane position (x and z-position) accuracy of core- exposed fiber is limited by the accuracy of microfabrication.
  • the channel may be set to a predetermined angle in the PIC plane with respect to the symmetric axis of the PIC waveguide. This ensures an intersection of the fiber waveguide with the PIC waveguide and drastically loosens the tolerance of the fiber in-plane position error.
  • the out-of-plane position (y-position) of the fiber is also well defined. The accuracy of the y-position is determined by the precision of both the depth of the channel and flat-to-core distance of the D
  • a linear polarized light is required to be maintained in the optical system.
  • the direction of the operation polarization is in the PIC plane. Since the polarization direction can be well maintained in both PIC and fiber waveguide by the respective birefringent waveguide designs, the polarization alignment accuracy in the coupling area is mainly dependent on the accuracy of the flat surface alignment of the D-fiber with the polarization axis of a polarization maintaining fiber.
  • the removal of the side cladding of the fiber can be carried out in pre-calibrated and controlled conditions to achieve an accurate flat surface alignment with respect to the fiber axis, by using a suitable method such as preform grounding followed by wet-etching of a D-shaped fiber, or laser ablation, or laser micro-drilling, or mechanical polishing of a PM fiber, among others.
  • the described procedure and apparatus facilitate a self-alignment between the optical fiber and the photonic integrated waveguide in all the six degrees of freedom; two-dimension (2D) in-plane position and the 2D tilt angle of the fiber are defined by the micro-fabricated channel, while the one-dimensional (1D) out-of-plane position and 1D polarization angle of the fiber are determined by the fiber flatness accuracy. Furthermore, the tapered PIC waveguide end and in-plane angled channel make the above-mentioned first five dimensions very insensitive to errors due to translation and angular misalignment. All these advantages facilitate a passive alignment. The assembling process can be automated with a high throughput.
  • the coupling efficiency is often sizably lower. For instance, if the same fiber and waveguide structures in FIG.9 are connected using end-fire coupling, and without a convertor or a focus lens, the maximum coupling efficiency is typically only about 39%.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)
  • Optical Couplings Of Light Guides (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)

Abstract

Selon l'invention, un dispositif optique comprend une fibre ayant une gaine et une âme, et un guide d'ondes PIC cible ayant une gaine et une âme. La gaine sur un côté de la fibre d'entrée est retirée à l'extrémité de la fibre et une surface plate est créée le long de l'âme de la fibre, à proximité de l'âme, exposant l'âme de la fibre. Un canal à fond plat possédant facultativement un angle en plan par rapport à l'axe symétrique du guide d'ondes PIC est fabriqué sur la couche supérieure du guide d'ondes PIC dans la zone de couplage, exposant la surface supérieure du guide d'ondes plan facultativement effilé. La surface plate de la fibre et la surface supérieure du guide d'ondes sont en contact, de telle sorte que l'âme de la fibre est coupée selon un angle par rapport à l'axe symétrique du guide d'ondes cible et à proximité l'un de l'autre au niveau de l'intersection en tant que région d'interaction pour définir un guide d'ondes hybride.
EP18786457.4A 2017-09-15 2018-09-13 Procédé et appareil de connexion à alignement automatique de fibre à un guide d'ondes de circuit intégré photonique Ceased EP3682276A1 (fr)

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US201762559307P 2017-09-15 2017-09-15
PCT/US2018/050896 WO2019055663A1 (fr) 2017-09-15 2018-09-13 Procédé et appareil de connexion à alignement automatique de fibre à un guide d'ondes de circuit intégré photonique

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KR20200060718A (ko) 2020-06-01
JP2020534566A (ja) 2020-11-26
US11092748B2 (en) 2021-08-17
US20190086614A1 (en) 2019-03-21
WO2019055663A1 (fr) 2019-03-21

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